Reed switch arrangement for dc magnetic circuit



Dec. 23, 1969 w Ms fio g ET AL. r 3,486,139

REED SWITCH ARRANGEMENT FOR DC MAGNETIC CIRCUIT Filed 001. 12, 1967FIG-2 FIG-1 I3 26 ,i i 75' v I f 25' I 1 1O 20 w 19 1 E I I I i IN l/E/VTORS GEORGE W. ARMSTRONG 8: ROBERT J. NEFF A TTOR/VE Y8 United StatesPatent US. Cl. 335-151 6 Claims ABSTRACT OF THE DISCLOSURE A reed switchis operated in response to the operation of a solenoid coil by forming aslit in the coils magnetic yoke and positioning the reed switch in thestray flux path formed at the slit.

BACKGROUND OF THE INVENTION In the application of Net]? and Armstrong,S.N. 587,132 filed Oct. 17, 1966, there are shown and claimedsolenoidoperated flow control valves and circuits in which a reed typeswitch is positioned in closely coupled relation to the magnetic fieldof the coil. The reed switches in that application operate as a holdingcircuit for the coil, and thereby eliminate the need for separatelyactuated relays. The invention disclosed therein has particular utilityfor use in circuits and apparatus disclosed and claimed in the US.patent of Armstrong et a1. 3,082,433 of Mar. 26, 1963.

In the preferred embodiment as shown and claimed in the Nelf andArmstrong application identified above, the reed switch is positionedaxially within the central opening of the solenoid so as to be subjectto the magnetic field of the coil. This arrangement while having manyadvantages over prior art devices, often, however, results in anincrease in the overall height of the coil. It also preferably utilizesa specially formed non-magnetic reed switch retainer, and pottingcompound or other means for securing the reed switch within itsretainer, adding somewhat to the cost of the device.

SUMMARY OF THE INVENTION The present invention is directed to thecombination of a reed switch and an electric solenoid having a magneticflux guide or yoke which lowers the reluctance of the return flux pathand therefore increases the efficiency of the solenoid. If a reed switchis positioned adjacent such a yoke it has been found that there isinsufiicient stray magnetic field to operate the switch. In the presentinvention, a discrete magnetic discontinuity is formed in the yoke at aposition adjacent the reed switch thereby forming a localized area ofhigh reluctance. Preferably, this discontinuity is formed simply bycutting a small transverse slot into the yoke at a location opposite theleaves of the reed switch. This has the effect of forming discretemagnetic poles across the slot gap when the solenoid coil is actuated bya source of DC current, thereby defining a localized stray magneticfield at the gap sufficient to 0perate the reed switch. This arrangementdoes not materially weaken the yoke nor does it materially reduce themagnetic effectiveness of the yoke, since only a small gap or cut isnecessary and since the magnetic leaves of the reed switch themselves,tend to form a path of relatively high permeability parallel to oracross the gap.

It is within the scope of the invention to form such a discretediscontinuity by any suitable means, effective for the intended purpose,such as by forming a localized groove transversely of the yoke. Further,if a complete slit or gap is formed, it may be desirable to fill the gap3,486,139 Patented Dec. 23, 1969 with non-magnetic material, such asepoxy or solder, in order to retain the integrity of the gap and preventit from being contaminated with iron filings or the like.

It is accordingly an important object of this invention to provide acompact reed switch arrangement for electric solenoids in which the reedswitch can be positioned between the yoke and the coil.

A further important object of this invention is the provision of a reedswitch arrangement in association with an electric solenoid having theusual magnetic yoke, in which a discrete magnetic discontinuity or alocalized area of high reluctance is formed adjacent to a reed switchfor operating the reed switch by the stray magnetic field formed at sucharea in response to the operation of the coil.

The invention thus has particular utility in use with DC operatedsolenoid flow control valves, as holding circuits for valves of thegeneral type disclosed in the above-identified Netf and Armstrongapplication.

These and other objects and advantages of the present invention will beapparent from the following description, the accompanying drawings andthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of asolenoid coil and reed switch arrangement constructed in accordance withthis invention;

FIG. 2 is a rear perspective view of the apparatus of FIG. 1; and

FIG. 3 shows the application of such a reed switch and solenoid coilcombination in a flow control valve incorporating a self-holdingcircuit.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings whichillustrate a preferred embodiment of the invention, a solenoid is shownin FIG. 1 as having an electric coil 10 with a generally C-shaped yoke12 partially encircling the coil 10. Thus, the yoke 12 has an upper leg13 which extends across the top of the coil, a back 15 which extendsdownwardly axially of the coil and a lower leg 16 which extends acrossthe bottom of the coil. The yoke is commonly made of suitable magneticmaterial, such as soft iron, forming a high permeability path exteriorlyof the coil for the return of flux from one end of the coil to theother. Commonly, such electric solenoids are formed with a centrallyaxially formed aperture 18 therethrough for accepting a suitablearmature, typical details of which are described in connection with thestructure of FIG. 3.

The electric coil 10 may be of any suitable cross-sectionalconfiguration, such as round, as sohwn, or octagonal. In eitherconfiguration, a generally wedge-shaped, axially aligning opening orclearance space is formed at 19 between the back 15 of the yoke 12 andthe adjacent surface of the coil. Two such openings 19 are formed at,one on either side of the center of the coil 10. This space is normallysufficient to receive a reed switch 20 wholly therein, and inwardly ofthe vertical edge of the back 15. A typical reed switch suitable forthis purpose may be the Form A by Hamlin, Inc., Lake Mills, Wis., andincludes a pair of spaced magnetic leaves 21 and 22 sealed within aglass envelope 23. When the switch is subject to a magnetic field, theleaves 21 and 22 form the opposite poles of the magnet and are thusattracted together closing the magnetic and electrical circuit throughthe switch 20.

We have found that a reed switch of the type defined above can beeffectively operated by positioning the switch axially within the recess19, and by forming in the back 15 of the yoke 12 a discrete magneticdiscontinuity adjacent the switch leaves, such as by cutting a shorttransverse slit 25 in the back. The slit 25 need only extendapproximately the width of the reed switch and may be formed with aquite narrow gap, such as inthe order of .010 inch, or less. However,the slit 25 preferably extends a width which is greater than thetransverse width of the switch 20 for ease in installing the switch but,as shown in FIG. 2, less than one-half of the width of the yoke back 15.The slit 25 thus defines in the yoke a discrete area of high magneticreluctance. When the coil is energized from a source of DC power,magnetic poles are formed across the gap defined by the slit 25 causinga localized area of stray flux at the gap sulficient to operate the reedswitch 20. The reed switch 20 may be held in position by insulatingtubular coverings 26 on the ends and on the leads and by wrapping withtape, or by potting in place with a suitable potting compound, asdescribed.

In FIG. 3 there is illustrated a pilot-valve or diaphragm type ofsolenoid-operated flow control valve 30 constructed according to thisinvention, in which like parts have been given like reference numeralsas used in FIGS. 1 and 2. Thus, it will be seen that the solenoid isformed with a central opening 18 defined by tubular magnetic inserts 31and 32 extending from the opposite ends of the opening 18, and anon-magnetic armature retainer 33 is positioned within the opening 18and includes a sliding magnetic armature and valve member 35 formed ofsuitable armature material.

A simplified holding circuit for the flow control valve is somewhatdiagrammatically illustrated in FIG. 3 as including a source of DC power36 connected to be applied to the coil 10 by a switch 37. The reedswitch 20 has its leads connected in parallel to the switch 37 through acircuit interrupting switch 38. Momentary closing of the switch 37directly energizes the coil 10. The stray field at the gap 25 closes theleaves 21 and 22 of the switch 20, forming a parallel holding circuitwhich will retain the coil, and the associated flow control valve in theoperated condition until such time as the circuit is interrupted to thereed switch in any known and suitable manner. The switch 38 may bemomentarily opened to break the holding circuit for the coil 10.

It is therefore seen that this invention provides a new combination ofmagnetic solenoid valve and reed switch which is compact since theswitch 20 is positioned wholly within the width of the yoke 12 betweenthe adjacent surface of the coil 10 and the inside surface of the yokeback 15.

The switch 20 is protected from damage by reason of its location betweenthe yoke back and the coil. Also the slit 25 extends only a shorttransverse distance across the back and does not materially weaken theyoke nor does it materially lessen the etfectiveness of the yoke as alow reluctance magnetic path. Also, the gap defined by the slit 25 canbe filled with a non-magnetic material to retain the strength of theyoke and to maintain the effectiveness of the gap, to prevent rust inthe gap and to prevent bridging by magnetic particles.

It is not necessary that the switch be used to control the supply ofcurrent to the coil 10. It may be used to control apparatus orindicators, such as an indicator light, at a remote point and at adifferent voltage than that used to operate the coil 10. Also, theswitch 20 may be for the sequential switching of a number of similarlyarranged units.

While the form of apparatus herein described constitutes a preferredembodiment of the invention, it is to be understood that the inventionis not limited to this precise form of apparatus, and that changes maybe made therein without departing from the scope of the invention whichis defined in the appended claims.

What is claimed is:

1. The combination of a reed switch and a solenoid coil in which saidcoil has a yoke extending substantially to the opposite ends thereofdefining a high permeability flux return path, the improvementcomprising a magnetically-operated reed-type switch positioned adjacentsaid yoke, and means in said yoke defining a discrete magneticdiscontinuity extending transversely of said return path partially thewidth of said yoke forming a localized region of relatively highmagnetic reluctance adjacent said reed switch while not materiallyaffecting the overall reluctance of said return path, said region ofhigh reluctance being' sufficient to cause a stray flux field to operatesaid reed switch when DC power is applied to the solenoid coil.

2. The combination of claim 1 in. which said discrete magneticdiscontinuity is defined by a transverse slit cut partially through saidyokel 3. The combination of claim 1 in which said yoke is generallyC-shaped with its opposite ends in overlying relation to the ends of thecoil and with a back extending adjacent one side of the coil in whichsaid discontinuity is formed in said back, and in which said reed switchis positioned inwardly of the outer edges of said back between said backand said coil with the leaves thereof adjacent said discontinuity.

4. The combination of a reed switch and a solenoid.

coil in which said coil has a yoke witha back portion extendingsubstantially to the opposite ends thereof defining a high permeabilityflux return path for said coil, the improvement comprising amagnetically-operated reed-type switch positioned adjacent said yokeback portion, and means in said back portion defining a slit adjacent areed switch extending transversely of said back portion a distance whichis substantially less than the Width thereof and forming a localizedregion of relatively high magnetic reluctance sufficient to cause astray flux field to operate said reed switch when DC power is applied tothe solenoid coil.

5. The combination of claim 4 in which said yoke is generally C-shapedwith its opposite ends in overlying relation to the ends of the coil andwith said back portion extending adjacent one side of the coil, and inwhich said reed switch is positioned inwardly of an outer edge of saidback portion between said back portion and said coil.

6. A combination of a reed switch and a DC operated electric solenoidvalve comprising a valve coil, a generally C-shaped magnetic flux returnyoke having opposite ends in overlying relation to the ends of the coiland a back extending adjacent one side of the coil, means on said backdefining a magnetic gap in the order of .010 inch across and having atransverse width which is less than half that of said back, and amagneticoperated reed-type switch positioned adjacent said gap foroperation with the application of DC current to said coil by thelocalized magnetic field formed at said gap.

References Cited UNITED STATES PATENTS 2,181,423 11/1939 Gille 335-251 X2,778,900 l/1957 Lenning 335-154 X 3,390,361 6/1968 Bodge 335-154 XBERNARD A. GILHEANY, Primary Examiner.

R. N. ENVALL, JR., Assistant Examiner

